Originally posted by Dericali I'm using 2x 64gb SD cards with 90mbs (or thereabouts) write speed.
What brand and model?
Worth noting, perhaps, that not all SD cards are what they claim to be ... Some measure their specifications very idiosyncratically, many cards are also simply counterfeit, particularly if bought online. Hence many a card may not perform as claimed.
Also did you format your cards in-camera? Remember that 64GB SD cards need to be formatted exFAT, vs FAT32 for 32 to 4GB GB cards. Formatting outside the camera (eg on a PC) can sometimes mess up the file system, which may compromise performance.